1. Field of the Invention
The present invention relates to a thermoplastic resin composition having improved melt-processability and particularly relates to a melt-processable aromatic polyimide resin composition and a readily melt-processable aromatic polysulfone resin composition, aromatic polyetherimide resin composition, aromatic polyamideimide resin composition and aromatic polyetherketone resin composition. More particularly, the invention relates to a thermoplastic resin composition having improved melt-processability obtained by mixing liquid crystal type aromatic polyimide with aromatic polyimide having excellent heat resistance, chemical resistance and mechanical strength, aromatic polysulfone having excellent mechanical strength, aromatic polyetherimide having excellent heat resistance, aromatic polyamideimide having excellent heat resistance and mechanical strength, or aromatic polyetherketone having excellent heat resistance and mechanical strength.
2. Prior Art of the Invention
Many thermoplastic resins having excellent heat resistance have been conventionally developed. In these resins, polyimide is excellent in mechanical strength and dimensional stability in addition to high heat resistance, and also has flame retardance and electrical insulation property. Thus, polyimide has been used in the fields of electric and electronic appliances, space ,and aeronautic equipment and transport machinery and is expected in the future to be used in various fields where heat resistance is required.
Various polyimides having excellent characteristics have been conventionally developed. Proger et al. have disclosed in U.S. Pat. No. 4,065,345 polyimide having recurring structural units of the formula (A): ##STR2##
The polyimide is excellent in mechanical property, thermal property, electrical property, solvent resistance and heat resistance, and has also been known as polyimide having melt-flowability. However, extrusion forming and injection molding of the polyimide is difficult because the polyimide has higher melt viscosity as compared with other common engineering plastics which can be extruded or injection molded.
The present inventors have also found polyimide which is excellent in mechanical properties, thermal property, electrical property and solvent resistance, has heat resistance, and has recurring structural units represented by the formula (B): ##STR3## wherein X is a radical selected from the group consisting of a direct bond, divalent hydrocarbon having 1.about.10 carbon atoms, hexafluorinated isopropylidene, carbonyl, thio and sulfonyl, and R is a tetravalent radical selected from the group consisting of an aliphatic radical having 2.about.27 carbon atoms, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or bridge member (Japanese Laid-Open Patent Sho 61-143478, 62-68817, 62-86021, 62-235381 and 63-128025).
The above polyimide resins are novel thermoplastic resins having good properties which are essential for polyimide.
For example, in the polyimide of the formula (B), polyimide having recurring structural units of the formula (6): ##STR4## has a glass transition temperature (hereinafter referred to simply as Tg) of 260.degree. C., crystallization temperature (hereinafter referred to simply as Tc) of 310.degree..about.340.degree. C. and crystal melting point (hereinafter referred to simply as Tm) of 367.degree..about.385.degree. C., and is crystalline polyimide which is melt processable and excellent in chemical resistance. However, a high temperature close to 400.degree. C. is required for processing the polyimide because of high Tm of 367.degree..about.385.degree. C.
Polyimide is much superior in heat resistance and other properties and still inferior in processability to common engineering plastics such as polyethylene terephthalate, polybutylene terephthalate, polyethersulfone, polysulfone, polyphenylene sulfide, polyether ether ketone and polyetherimide.
Some known polyimide has no distinct glass transition temperature though excellent in heat resistance and hence must be processed by such means as sinter molding when the polyimide is used for a molding material. Other known polyimide has a low glass transition temperature and is soluble in halogenated hydrocarbon solvent though excellent in processability and hence is unsatisfactory in view of resistance to heat and solvent. Both merits and drawbacks have thus been found in the properties of known polyimide.
Further, aromatic polysulfone, aromatic polyetherimide, aromatic polyamideimide and aromatic polyether ketone are excellent in mechanical strength and dimensional stability in addition to high heat resistance and also have flame retardance and electrical insulation property. Thus, these plastics are used in the field of electric and electronic appliances, space and aeronautic equipment and transport machinery and are expected to be used in various fields in the future where heat resistance is required. Aromatic polysulfone is an engineering plastic having good processability. However, aromatic polyetherimide, aromatic polyamideimide and aromatic polyether ketone which are called super engineering plastics have problems in processability and are desired to have good processability while maintaining high heat resistance.
On the other hand, liquid crystal type high polymers are classified into thermotropic liquid crystal and lyotropic liquid crystal. Conventionally known liquid crystal type high polymers are polyester, polyesteramide and polyazomethine which are thermotropic liquid crystals and polyamide and polybenzothiazole which are lyotropic liquid crystals. However, polyimide exhibiting liquid crystal property has been quite unknown.
Consequently, a resin composition obtained by mixing liquid crystal type polyimide with polyimide or other thermoplastic resins has been quite unknown.